The present invention relates to a method of executing a three-dimensional measurement for measuring dimension of a measureable object such as an automotive body or a press mold or the like. More particularly, the invention relates to a method of measuring a three-dimensional dimension of a workpiece mounted on an objective position by providing a plurality of CCD cameras in position close to a measurable object.
When directly measuring dimension of a measurable workpiece A having cubic configuration like an automotive body in an assembly factory in place of a laboratory equipped with a variety of measuring instruments, normally, such a conventional method described below is executed.
As shown in FIG. 3, initially, a measuring jig B is secured to a predetermined measuring position in order to stably hold an objective workpiece A. Next, the objective workpiece A is positioned on the measuring jig B. At the same time, a pair of theodolites 1 and 2 are set to predetermined positions in front of a measurable surface of the positioned workpiece A.
Each of these theodolites 1 and 2 incorporates a high-precision telescope which is swingably held in the horizontal and vertical directions. When the measurable target point is caught in the center of the telescopic lens, horizontal and vertical angles of the telescope are externally displayed.
To securely measure dimensions of the measurable workpiece A in presence of the above condition, initially, a plurality of reference-point members C needed for determining positional relationship between a pair of theodolites 1 and 2 and the measurable workpiece A are installed to at least four locations in the periphery of the measurable workpiece A positioned on the measuring jig B. In addition, a reference bar F is placed on the positioned workpiece A or at any optional position in the periphery of the measurable workpiece A. The reference bar F has a known distance L between a pair of points D and E.
Next, a pair of theodolites 1 and 2 are activated to sequentially measure positions of a plurality of reference-point members C. In the meanwhile, those theodolites 1 and 2 sequentially transmit horizontal and vertical directional data to a computer system (not shown). After completing those sequential processes, the theodolites 1 and 2 respectively measure positions of a pair of points D and E of the reference bar F before transmitting those position data to the computer system. On receipt of those position data covering 6 points measured by those theodolites 1 and 2, based on these position data, the computer system computes relative positions and postures of those theodolites 1 and 2, and then, based on the position data, the computer system computes relative positions and postures of these theodolites 1 and 2, and then, based on the distance data L between a pair of points D and E of the reference bar F, the computer system computes absolute positions and postures of the theodolites 1 and 2.
After correctly identifying absolute positions and postures of those theodolites 1 and 2 set in front of the measurable workpiece A, these theodolites 1 and 2 sequentially measure predetermined positions on the surface of the workpiece A, and then, the computer system processes positional data of respective points via triangulation before completing measurement of three-dimensional dimension of the measurable workpiece A. FIG. 4 presents an operational flowchart of those sequential processes described above.
As mentioned above, by properly operating a pair of theodolites 1 and 2 and a computer system needed for processing positional data measured by those theodolites 1 and 2, three-dimensional dimension of an objective workpiece A can be measured in a factory that manufactures the workpiece A.
Nevertheless, when actually measuring dimension of an objective workpiece A in the factory, unwanted vibration is unavoidably transmitted to the floor of the measuring location from a variety of machine tools, factory workers walking around the measuring location, and workpiece carriers.
Because of this, positional relationship between those theodolites 1 and 2 and the objective workpiece A is easily variable to result in the significantly degraded measuring precision, thus causing critical problems.
In an extreme case, while those who are in charge of executing dimensional measurement are not aware of, factory workers or workpiece carriers may come into contact with either of those theodolites 1 and 2 or the measurable workpiece A to significantly vary the positional relationship between these. In consequence, abnormal result will be generated to oblige the measuring staff to repeatedly execute the three-dimensional measuring operation.